I ship my Drosera by removing most of the medium, trying to keep a little attached to the roots. I then lay the plant on a small amount of flattened live LFS, and roll it or bunch it up so that the roots and top of the plant are enclosed in it. I then roll this inside a strip of wet unbleached paper towel, and the resulting roll is placed in a small ziplock bag and labeled. It should not be overly wet, but if you squeezed it hard a few drops of water would drip. I stuff a box on the bottom with old plastic grocery bags, and lay the ziplock/s on top. Then I add more to the top and sides so that there can be no motion of the contents. Aim for a box that you can easily fill the space with packing. Space is the enemy. I have found shipping potted plants is a difficult process, and try to avoid it. The pots cause more problens than they are worth and makes me appreciate the efforts PFT places into shipping their potted material!
I have learned that pygmy gemmae are best shipped by placing them in a small zip lock bag loosley, adding 3 drops of water and zipping the bag. They actually arrive healthier, and if they root in the travel interm they are more easily removed and planted. I have lost several species because they rooted into the wet paper, or suffocated.
Seeds should have some sort of padding, otherwise they can be crushed by the stamp cancellation machines. A bit of bubble wrap or paper toweling is needed.
Utricularia ship ok by the same method as for the sundews.
Sarracenia need their roots to stay a bit wet, so very sodden paper towels are needed about the roots.
Heliamphora are brittle and must be totally immobile.
Neps I can't speak for, but I would think similar to Sarracenia.
Pings vary too greatly to make any general recommendation. Some need to stay moist, others need to be barely moist.
In all cases you must consider the length of travel time in regards to how wet to ship your plants. I always use priority mail, and feel anticipating a week in the post via this method is not overly pessimistic since many times it has taken that long if the mails are busy. I have had more plants die from drying out than arriving wet.
Hope this helps.